The application generally relates to sizing of cooling holes on turbine components. The application relates more specifically to an electrospark deposition (ESD) process for reducing oversized holes in gas turbine engine components.
Electrospark deposition (ESD) is a pulsed-arc, micro-welding process that uses short-duration, high-current electrical pulses to deposit a consumable electrode material on a conductive workpiece. ESD processes generally involve very high spark frequencies with the spark duration lasting only a few microseconds. ESD generally requires manual control or preprogramming of the process parameters. Significantly, depositions result in very little heat input because heat is generated during less than 1% of a weld cycle and dissipated during 99% of the cycle. ESD coatings are extremely dense and metallurgically bonded to the workpiece. Conventional electrospark deposition devices employ an electrode rod, which is required to have a sharp tip for generating electrical discharges or sparks. When using conventional ESD devices it is difficult to repair or build up confined surfaces such as an inner diameter of a hole in a metal part.
Many component parts of a gas turbine engine include cooling holes for active cooling of engine sections located downstream of the turbine section. The rising combustor exit temperatures in gas turbine engines necessitate active cooling to avoid thermal failure. In some parts of the gas turbine engine, hole dimensions are not as important, but cooling hole configurations may be critical on such parts as buckets, vanes, shrouds and nozzles, for example.
In manufacturing gas turbine component parts, drilling and machining operations may on occasions result in cooling holes being larger than specified, e.g., when an incorrect hole diameter is used when setting up the tooling, or when an operator error occurs during manufacturing. When a hole drilled in an engine component is too large, the component may not pass inspection, and will be returned for quality control reasons for correction. Currently, repair of oversized holes may be a costly and time consuming project, and may not be possible at all, resulting in the loss of valuable engine parts. Oversizing of holes can occur during turbine operation due to erosion, oxidation, and other operational conditions.
Currently, one solution for dealing with oversized cooling holes in engine components is to weld the oversized holes until they are closed, and machine new cooling holes in the engine component using electrode discharge machining (EDM) process. EDM is a process whereby material is removed from the workpiece by a series of rapidly recurring current discharges between an electrode and the workpiece, separated by a dielectric liquid and subject to an electric voltage.
Intended advantages of the disclosed systems and/or methods satisfy one or more of these needs or provide other advantageous features. Other features and advantages will be made apparent from the present specification. The teachings disclosed extend to those embodiments that fall within the scope of the claims, regardless of whether they accomplish one or more of the aforementioned needs.